1. Field of the Invention
The present invention relates to a new and improved press section of a papermaking machine for pressing and dewatering a paper web.
Generally speaking, the press section of a papermaking machine for dewatering a paper web, as contemplated by the present development, is of the type comprising two separate successively arranged press locations. Each press location is formed between an upper extended press surface and a lower extended press surface forming extended or wide press nips. The press section contains at the first press location and at the second press location at least one respective separate felt guided in conjunction with the paper web through the press locations. The second press location contains a cylindrical counter roll or roller extending essentially beneath the second press location and an extended nip press roll extending essentially above the second press location. This extended nip press roll forms the extended nip of the second pres location and is essentially accommodated to the contour of the counter roll.
2. Discussion of the Background and Material Information
Press sections or press arrangements of the aforementioned type for pressing and dewatering a paper web possess the decisive advantage that by using press structures which, as viewed in the direction of travel of the paper web, have an extended or wide press length, that is, an extended press nip, there is available a relatively large amount of time for expressing liquid out of the paper web. As a result, such a press section can operate with relatively few press locations and nonetheless can achieve a high dewatering effect or capacity even with relatively rapid throughpass or high speed travel of the paper web. The presently known press apparatuses or arrangements containing an extended press nip are frequently constructed such that there is provided a press roll equipped with a flexible shell or jacket which is pressed from internally of the press roll by means of an essentially only radially movable press element against a rigid counter roll, and the flexible shell or jacket, at the region of the extended press nip, can snugly bear against the rigid counter roll. However, other constructions are possible for achieving an extended press nip or press surface.
In order to obtain as great as possible operational reliability of the press section, at high speed papermaking machines it is strived to continuously maintain the paper web in contact with at least one felt, in order to thus avoid a so-called free or open draw where the paper web would be exposed to the danger of tearing. What is disadvantageous with such arrangements is especially that, following departure of the paper web from the press nip, there occurs remoistening or rewetting of the paper web by the water entrained by the felt.
In the commonly assigned German Published Patent Application No. 3,742,848, published Jun. 29, 1989, and the cognate U.S. Pat. No. 4,915,790, granted Apr. 10, 1990, there is disclosed an arrangement intended to solve the aforementioned problem, wherein special measures are undertaken in order to raise at least one felt very rapidly away from the paper web after the latter emerges from the press nip.
Furthermore, solutions have become known in the papermaking art where only a single felt is present in the second press nip. If this felt is located at the top of the paper web, then such paper web can drop off such felt much too easily prior to entering the second press location or press nip. On the other hand, if such felt is located at the bottom of the paper web, especially in the form of a continuous felt which spans both press locations or press nips, then the paper web co-travels throughout its full width, following exit from the second press location or press nip, upwardly together with the top or upper roll, and is then difficult to handle. Moreover, at this location there also exists a greater tendency of the paper web to again suck up water from the felt behind the press nip.
German Published Patent Application No. 3,815,278, published Nov. 16, 1989, discloses a press arrangement containing two successive roll presses each provided with an extended press nip. While here there exist favorable conditions for dewatering the paper web, on the other hand, the paper web is transported by one felt through both roll presses or press locations. It is not possible to condition the paper web between both of the roll presses.